1. Field of the Invention
This invention relates generally to fabricating integrated circuit packages, and in particular, to an apparatus and method that controls unwanted spreading of adhesive used to attach semiconductor integrated circuit dies to an integrated circuit package assembly.
2. Description of the Related Technology
The semiconductor integrated circuit has revolutionized the field of electronics by becoming a basic building block in electronic products. The integrated circuit has made it possible to create many new electronic products and related services in the consumer, industrial and military markets. As more and more electronic products were introduced, a great demand for the integrated circuits used to build these products was created.
This demand resulted in a new industry devoted to manufacturing semiconductor integrated circuits in quantity and at a price that was acceptable in the various electronic markets. In order to keep the price of integrated circuits as low as possible, assembly line, automation and large quantity manufacturing techniques were required.
Packaging techniques for integrated circuits have been developed to satisfy demands for miniaturization in the semiconductor industry. Improved methods for miniaturization of integrated circuits enabling the integration of millions of transistor circuit elements into single integrated silicon embodied circuits, or chips, have resulted in increased emphasis on methods to package these circuits in space efficient, yet reliable and mass producible packages.
Integrated circuits are created from a silicon wafer using various etching, doping and depositing steps that are well known in the art of fabricating integrated circuit devices. A silicon wafer is comprised of a number of integrated circuit dies that each represent a single integrated circuit chip. Ultimately, the die or chip may be packaged by transfer molding plastic encasement around the die with a variety of pin-out or mounting and interconnection schemes. For example, M-Dip (Dual-In-Line-Plastic) provides a relatively flat, molded package having dual parallel rows of leads extending from the bottom for through-hole connection, and mounting to an underlying printed circuit board. More compact integrated circuits allowing greater density on a printed circuit board are the SIP (Single-In-Line-Plastic), PLCC (Plastic Leaded Chip Carrier), and SOJ (Small Outline J-leaded) molded case packages.
Integrated circuits are comprised of many interconnected transistors and associated passive circuit elements that perform a function or functions. These functions may be random access memory, central processing, communications, etc. Different types of integrated circuits are used to create an electronic system such as a personal computer. Combining integrated circuits requires electrically connecting each integrated circuit together to form the electronic system. Once the integrated circuits are connected together in a system, other devices such as keyboards, video monitors and printers may be connected to and utilized with the system.
In order to accomplish this interconnection, conductive paths must be made available to connect the internal circuitry of the integrated circuit die to external system electrical circuits. The integrated circuit die uses metallized bumps or "bond pads" which are connected to the internal circuits of the die.
The integrated circuit package has conductors called "bond fingers" that are connected to the bond pads of the integrated circuit die by wire bonding, tape automated bonding ("TAB"), wedge bonding, ball bonding or other methods well known in the art. The bond fingers are connected to the integrated circuit package pins that are used to connect to printed circuit boards.
Before the integrated circuit die bond pads are connected to the integrated circuit package, the die must be mechanically attached to the package assembly. Epoxy adhesive containing silver filler particles may be used for attachment of the die to the package assembly. Epoxy adhesive, however, spreads or "bleeds" away from the adhesion area. Both the silver filled epoxy and the epoxy resin base spread or bleed away from the die and package mounting area. Any filled epoxy or epoxy resin that flows onto a bond finger contaminates this bond finger and may result in a defective wire bond thereto.
To control the epoxy from spreading or bleeding onto the bond fingers, the die and adhesive may be recessed into a cavity. The bond fingers adjacent to the die are placed above the surface of the die attachment cavity and this cavity substantially prevents epoxy from spreading or bleeding onto bond fingers above. Integrated circuit package assemblies requiring a large number of pins such as, for example, those using very large scale integrated (VLSI) circuit dies, do not always have the option of an attachment cavity. These VLSI package assemblies have the bond fingers at the same level as the die attachment surface.
What is needed in fabricating VLSI semiconductor integrated circuit dies with corresponding high density packages is a way to prevent adhesive spreading of the die attachment epoxy onto the adjacent bond fingers when both are on the same surface plane.